A liquid crystal display device has been widely used as a thin, light-weight, and low power consumption display device. A liquid crystal panel included in the liquid crystal display device has a structure formed by attaching an active matrix substrate and a counter substrate together, and providing a liquid crystal layer between the two substrates. A plurality of gate lines, a plurality of data lines, and a plurality of pixel circuits each including a thin film transistor (hereinafter referred to as a TFT) and a pixel electrode are formed on the active matrix substrate.
As a system for applying an electric field to the liquid crystal layer of the liquid crystal panel, a vertical electric field system and a lateral electric field system are known. In a liquid crystal panel of the vertical electric field system, an almost vertical electric field is applied to the liquid crystal layer by using the pixel electrode and a common electrode formed on the counter substrate. In a liquid crystal panel of the lateral electric field system, the common electrode is formed on the active matrix substrate together with the pixel electrode, and an almost lateral electric field is applied to the liquid crystal layer by using the pixel electrode and the common electrode. The liquid crystal panel of the lateral electric field system has an advantage of having a wider view angle than that in the liquid crystal panel of the vertical electric field system.
As the lateral electric field system, an IPS (In-Plane Switching) mode and an FFS (Fringe Field Switching) mode are known. In a liquid crystal panel of the IPS mode, the pixel electrode and the common electrode are each formed in the shape of comb teeth, and are disposed so as not to overlap each other in a plan view. In a liquid crystal panel of the FFS mode, a slit is formed either in the common electrode or the pixel electrode, and the pixel electrode and the common electrode are disposed so as to overlap each other via a protective insulating film in a plan view. The liquid crystal panel of the FFS mode has an advantage of having a higher aperture ratio than that in the liquid crystal panel of the IPS mode.
The liquid crystal panel of the lateral electric field system is described in Patent Documents 1 and 2, for example. In the liquid crystal panels described in Patent Documents 1 and 2, the common electrode is formed corresponding to almost all of a display region (except for the slit and the like). The common electrode is formed in a layer over the data line, with an insulating film interposed therebetween. The pixel electrode and a drain electrode of the TFT are directly connected to each other without interposing a contact hole formed in the insulating film. Patent Documents 1 and 2 also describe a method for manufacturing the active matrix substrate, the method including a step for forming a channel region of the TFT while forming the pixel electrode.
FIG. 20 is a layout diagram described in FIG. 8 of Patent Document 1. FIG. 21 is a layout diagram described in FIG. 2 of Patent Document 2. In FIGS. 20 and 21, a left down oblique line part represents a gate layer pattern, a right down oblique line part represents a source layer pattern, and a thick line Ex represents an edge of the pixel electrode. In order to facilitate comparison with drawings of the present application, notations in FIGS. 20 and 21 are changed from those in the original drawings.
In FIG. 20, a data line 92 has a portion functioning as a source electrode (a portion protruding rightward in the drawing). A TFT is formed by providing a drain electrode 93 opposing to the source electrode, and the like. A pixel electrode 94 has an extension part (a portion protruding downward in the drawing), and the extension part of the pixel electrode 94 overlaps with a gate line 91. In FIG. 21, a data line 96 has a portion functioning as a source electrode (a portion protruding rightward in the drawing). A TFT is formed by providing a drain electrode 97 opposing to the source electrode, and the like. A pixel electrode 98 has an extension part (a portion protruding downward in the drawing), and the extension part of the pixel electrode 98 overlaps with a gate line 95.